Dover
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dover clear sky chart from 2005-11-05 to 2017-09-18.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.
Observation TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(no limit)Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
41%
15198
21%
46881
12%
15162
51%
15162
27%
29208

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 15thNight
26%
718
22%
2500
10%
716
43%
716
21%
1525
January16th to endNight
24%
768
23%
2496
8%
768
42%
768
25%
1528
February1st to 15thNight
23%
704
20%
2255
9%
701
39%
701
23%
1399
February16th to endNight
21%
631
26%
1893
8%
631
44%
631
25%
1161
March1st to 15thNight
30%
720
21%
2082
10%
720
43%
720
28%
1318
March16th to endNight
29%
768
21%
2037
9%
768
39%
768
27%
1366
April1st to 15thNight
33%
718
20%
1796
7%
718
39%
718
32%
1179
April16th to endNight
41%
720
20%
1800
8%
720
46%
720
32%
1186
May1st to 15thNight
40%
555
17%
1635
10%
555
46%
555
24%
1124
May16th to endNight
54%
374
16%
1497
15%
374
59%
374
20%
916
June1st to 15thNight
55%
360
17%
1440
17%
360
61%
360
23%
846
June16th to endNight
62%
360
16%
1440
20%
360
66%
360
26%
827
July1st to 15thNight
62%
340
14%
1360
18%
340
64%
340
21%
838
July16th to endNight
67%
447
17%
1483
17%
419
71%
419
29%
840
August1st to 15thNight
68%
590
19%
1660
13%
587
69%
587
33%
1027
August16th to endNight
67%
764
19%
1910
12%
764
68%
764
37%
1235
September1st to 15thNight
57%
720
25%
1800
15%
720
61%
720
34%
1190
September16th to endNight
57%
669
24%
1806
20%
669
59%
669
31%
1161
October1st to 15thNight
49%
660
24%
1980
20%
660
56%
660
29%
1239
October16th to endNight
38%
704
27%
2126
17%
704
52%
704
31%
1249
November1st to 15thNight
39%
700
23%
2277
15%
700
52%
700
28%
1357
November16th to endNight
33%
720
22%
2400
13%
720
46%
720
23%
1475
December1st to 15thNight
28%
720
19%
2520
8%
720
42%
720
21%
1571
December16th to endNight
26%
768
22%
2688
9%
768
44%
768
21%
1651

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

Occurrence of each ForecastData
Points
Cloud CoverDay
13%5%2442445%7%43%
47913
Night
14%5%2442445%7%43%
47058
Cloud CoverDay
13%5%2442445%8%43%
47922
Night
14%5%2442445%7%43%
47064
TransparencyDay
37%5%12%24%16%2
47608
Night
39%411%23%17%3
46881
SeeingDay
16%422%26%20%8%
5779
Night
17%6%27%31%14%1
15201

By Month

Percentage Cloud Cover NE (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
12%7%3442336%7%44%
1436
16th to endDay
16%5%24324346%45%
1728
February1st to 15thDay
14%7%25%31445%6%43%
1606
16th to endDay
12%7%35%424446%42%
1580
March1st to 15thDay
15%5%25%424446%43%
1868
16th to endDay
17%5%24325%44444%
2187
April1st to 15thDay
14%5%2442345%6%45%
2152
16th to endDay
14%424423447%45%
2160
May1st to 15thDay
16%425%4245%5%8%40%
2325
16th to endDay
13%424425%5%6%8%42%
2618
June1st to 15thDay
11%3245%35%6%7%9%40%
2520
16th to endDay
9%4245%25%47%10%44%
2520
July1st to 15thDay
8%5%24435%6%7%9%42%
2520
16th to endDay
5%325%6%36%7%9%11%38%
2580
August1st to 15thDay
10%5%245%345%6%9%42%
2277
16th to endDay
9%4245%35%5%6%9%43%
2292
September1st to 15thDay
12%4235%2446%8%45%
2160
16th to endDay
15%6%25%5%35%45%6%40%
1876
October1st to 15thDay
17%41433245%6%45%
1650
16th to endDay
15%424323246%49%
1744
November1st to 15thDay
16%5%23324336%46%
1581
16th to endDay
14%5%2343435%7%45%
1557
December1st to 15thDay
15%425%5%24447%43%
1440
16th to endDay
18%6%24424447%40%
1536
January1st to 15thNight
17%5%2442445%6%43%
2500
16th to endNight
16%6%25%313446%43%
2496
February1st to 15thNight
14%7%25%423445%43%
2254
16th to endNight
15%6%23424345%47%
1893
March1st to 15thNight
16%6%24314446%45%
2069
16th to endNight
17%6%25%5%23435%42%
2037
April1st to 15thNight
15%6%24424346%45%
1796
16th to endNight
17%42433335%7%43%
1800
May1st to 15thNight
17%8%36%32445%7%36%
1635
16th to endNight
13%5%25%5%25%5%5%10%38%
1495
June1st to 15thNight
13%425%5%235%5%9%42%
1440
16th to endNight
8%435%5%245%7%10%42%
1440
July1st to 15thNight
7%425%5%46%6%7%9%38%
1440
16th to endNight
6%425%5%25%6%7%10%42%
1585
August1st to 15thNight
6%4245%25%5%6%9%44%
1671
16th to endNight
10%42443446%8%44%
1910
September1st to 15thNight
13%5%14424446%46%
1800
16th to endNight
16%5%144245%47%43%
1806
October1st to 15thNight
17%424413346%46%
1980
16th to endNight
14%413323436%50%
2126
November1st to 15thNight
14%5%35%323345%49%
2277
16th to endNight
14%5%244245%5%6%42%
2400
December1st to 15thNight
17%5%25%43445%6%40%
2520
16th to endNight
17%5%2442445%6%42%
2688

Percentage Cloud Cover SE (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
13%7%3443335%7%44%
1436
16th to endDay
17%5%24323446%45%
1728
February1st to 15thDay
14%7%25%314446%43%
1606
16th to endDay
12%7%35%4245%47%42%
1580
March1st to 15thDay
15%5%2442345%6%43%
1878
16th to endDay
17%5%24324445%43%
2186
April1st to 15thDay
14%42342345%6%46%
2152
16th to endDay
14%4244235%47%45%
2160
May1st to 15thDay
16%4245%245%48%40%
2325
16th to endDay
13%4244245%6%8%43%
2618
June1st to 15thDay
11%4245%35%6%7%9%40%
2520
16th to endDay
9%42342447%10%44%
2520
July1st to 15thDay
9%5%24435%5%7%9%42%
2520
16th to endDay
6%325%5%46%7%8%10%38%
2580
August1st to 15thDay
10%5%25%4345%6%8%42%
2277
16th to endDay
8%424435%5%6%8%43%
2292
September1st to 15thDay
12%42442446%8%44%
2160
16th to endDay
15%5%25%5%35%5%46%40%
1876
October1st to 15thDay
18%32432346%7%45%
1650
16th to endDay
16%5%23323346%49%
1744
November1st to 15thDay
16%6%23324336%46%
1581
16th to endDay
14%41443345%7%45%
1557
December1st to 15thDay
15%4245%34447%43%
1440
16th to endDay
18%6%24424347%40%
1536
January1st to 15thNight
17%5%245%24446%43%
2500
16th to endNight
17%6%34313445%44%
2496
February1st to 15thNight
14%7%35%423445%43%
2247
16th to endNight
15%5%23424345%47%
1893
March1st to 15thNight
16%6%24313447%45%
2082
16th to endNight
17%6%25%433336%42%
2037
April1st to 15thNight
15%5%24424346%44%
1796
16th to endNight
18%42432336%6%44%
1800
May1st to 15thNight
17%7%35%32445%7%37%
1635
16th to endNight
13%5%25%5%35%45%9%38%
1495
June1st to 15thNight
13%3245%2446%9%42%
1440
16th to endNight
8%435%5%245%6%10%42%
1440
July1st to 15thNight
8%426%5%46%6%7%9%39%
1440
16th to endNight
6%425%5%25%6%7%11%42%
1585
August1st to 15thNight
7%4345%35%5%7%9%44%
1671
16th to endNight
10%425%33445%8%44%
1910
September1st to 15thNight
13%5%24424446%46%
1800
16th to endNight
16%41432445%7%43%
1806
October1st to 15thNight
18%5%24422346%46%
1980
16th to endNight
15%413323346%50%
2126
November1st to 15thNight
14%5%34313345%49%
2277
16th to endNight
15%5%244245%5%6%43%
2400
December1st to 15thNight
17%5%25%42445%6%40%
2520
16th to endNight
17%5%2442445%6%42%
2688

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
39%215%23%13%4
1437
16th to endDay
40%310%26%16%3
1728
February1st to 15thDay
40%313%25%14%2
1609
16th to endDay
41%310%27%13%2
1580
March1st to 15thDay
40%312%24%16%2
1878
16th to endDay
41%5%9%22%17%3
2187
April1st to 15thDay
38%311%25%16%5%
2152
16th to endDay
39%311%19%21%5%
2160
May1st to 15thDay
39%5%15%21%16%1
2325
16th to endDay
37%5%16%25%13%1
2622
June1st to 15thDay
36%8%14%26%12%1
2520
16th to endDay
32%6%16%23%18%1
2520
July1st to 15thDay
35%7%12%25%14%3
2371
16th to endDay
32%9%16%25%14%1
2419
August1st to 15thDay
37%5%13%27%14%1
2264
16th to endDay
33%6%14%23%17%4
2292
September1st to 15thDay
35%412%23%20%2
2160
16th to endDay
41%48%19%23%2
1876
October1st to 15thDay
37%312%27%16%2
1650
16th to endDay
37%28%29%19%2
1744
November1st to 15thDay
39%310%24%18%3
1581
16th to endDay
38%310%27%16%3
1557
December1st to 15thDay
40%415%24%11%2
1440
16th to endDay
44%313%24%13%1
1536
January1st to 15thNight
42%311%21%18%3
2500
16th to endNight
41%211%26%16%1
2496
February1st to 15thNight
42%210%25%16%2
2255
16th to endNight
38%29%24%20%3
1893
March1st to 15thNight
40%311%25%17%2
2082
16th to endNight
44%210%20%18%3
2037
April1st to 15thNight
40%29%22%19%4
1796
16th to endNight
39%49%20%20%6%
1800
May1st to 15thNight
46%49%21%15%2
1635
16th to endNight
41%6%14%19%14%2
1497
June1st to 15thNight
38%6%12%23%16%1
1440
16th to endNight
35%6%14%23%16%2
1440
July1st to 15thNight
39%8%15%19%12%3
1360
16th to endNight
31%8%17%26%14%1
1483
August1st to 15thNight
34%6%15%23%18%1
1660
16th to endNight
35%413%22%20%2
1910
September1st to 15thNight
37%5%9%24%19%3
1800
16th to endNight
38%48%22%22%3
1806
October1st to 15thNight
39%39%25%17%3
1980
16th to endNight
36%38%29%19%3
2126
November1st to 15thNight
37%310%22%17%7%
2277
16th to endNight
40%410%24%17%3
2400
December1st to 15thNight
43%312%24%13%2
2520
16th to endNight
42%313%24%14%2
2688

Seeing (when cloud cover <= 80%)
Color Meanings:
Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
13%16%42%16%9%1
61
16th to endDay
27%14%34%14%9%
96
February1st to 15thDay
23%14%33%24%4
123
16th to endDay
14%12%44%24%4
239
March1st to 15thDay
17%11%30%31%8%
270
16th to endDay
18%6%38%23%9%3
288
April1st to 15thDay
19%5%34%25%11%3
270
16th to endDay
20%5%22%26%21%4
270
May1st to 15thDay
25%7%29%19%13%4
288
16th to endDay
19%114%26%27%11%
331
June1st to 15thDay
15%217%29%22%11%
315
16th to endDay
10%118%33%28%7%
315
July1st to 15thDay
10%311%32%31%10%
305
16th to endDay
6%28%31%37%14%
326
August1st to 15thDay
14%11%26%31%15%
313
16th to endDay
9%6%30%32%20%
332
September1st to 15thDay
15%118%22%25%16%
315
16th to endDay
21%215%27%18%14%
262
October1st to 15thDay
20%119%27%21%9%
255
16th to endDay
14%8%28%29%17%1
269
November1st to 15thDay
16%330%27%17%4
235
16th to endDay
15%7%36%23%14%2
177
December1st to 15thDay
15%13%28%26%11%5%
60
16th to endDay
39%6%28%18%7%
64
January1st to 15thNight
19%12%35%26%6%
720
16th to endNight
20%9%39%27%2
768
February1st to 15thNight
18%11%41%26%2
704
16th to endNight
17%14%41%22%3
631
March1st to 15thNight
18%8%37%28%6%
720
16th to endNight
18%7%37%25%8%1
768
April1st to 15thNight
18%6%37%30%6%
718
16th to endNight
19%6%26%34%13%
720
May1st to 15thNight
21%5%24%35%11%1
555
16th to endNight
16%216%39%23%2
375
June1st to 15thNight
15%117%40%23%1
360
16th to endNight
8%315%49%22%
360
July1st to 15thNight
9%213%42%30%1
340
16th to endNight
7%210%40%36%3
447
August1st to 15thNight
9%19%45%31%2
590
16th to endNight
14%17%39%31%5%
764
September1st to 15thNight
15%215%34%29%3
720
16th to endNight
19%113%33%26%5%
669
October1st to 15thNight
21%318%34%18%3
660
16th to endNight
18%6%31%27%14%
704
November1st to 15thNight
17%5%30%29%14%2
700
16th to endNight
17%11%31%27%10%1
720
December1st to 15thNight
23%7%35%22%10%1
720
16th to endNight
19%9%39%28%3
768
Page generated at 2017-09-19 07:32:21. Version ac04

Copyright 2017 A. Danko


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